In recent years, microwave ovens have become increasingly popular. This has created an increasing demand for economical, simple, disposable containers which, when used in a microwave oven, produce cooking results, including surface browning and crisping, comparable to those to which people are accustomed to experiencing with conventional ovens. For consumer convenience, it is desirable that the package be constructed so that the food item, together with all or a portion of the package, can be placed directly in the oven.
Paperboard cartons have been found to be an economical way to meet many microwave packaging requirements. In particular, a number of cartons for browning microwave foods have been successfully sold that are made from paperboard to which a metallized plastic film has been laminated, with the thin metallized layer being sandwiched between the plastic film and the paperboard. A suitable adhesive is used to hold the laminated layers together. One laminated material of this kind is shown in U.S. Pat. No. 4,641,005.
Although microwave browning packages of several kinds are now widely sold and the surface browning capability of a metallized film-paperboard laminate used in such packages is widely accepted, the effect of unusual food and package shapes, of multiple layers of microwave absorbing materials and of other specialized package configurations on cooking results is not well understood. This is apparently attributable to the complex combination of reflections, refractions and absorptions of microwave radiation occuring in the oven, the food and the packaging. It is also attributable to the different way in which microwaves cook food, as compared to the heating modes of conventional ovens. Accordingly, development of specific package configurations has proceeded slowly and empirically, as the microwave cooking possibilities of various food items are explored. Each food item and each packaging configuration seems to have its own cooking characteristics.
Many of the microwave cooking packages first developed were for products such as pizza and popcorn. Because of their specialized configuration, such as suitability for cooking flat dough or for maintaining popcorn kernels in a pool of hot oil, these packages are not effective for food items that requires browning on a curved surface. Accordingly, there is a need for packaging for effective microwave cooking of a food item having elongated curved surfaces, such as egg rolls, sausages and other similarly cylindrical items.